This invention relates to a tracking or training idler assembly which is typically although not exclusively adapted to track a trough shaped belt.
It is well known that conveyor belts tend to drift or creep sideways as they travel along their intended paths. The problem is exacerbated where the belt is particularly long, carries a high load, or is a particularly heavy belt. The problem is further compounded on the load carrying side of the belt where the load is not centrally located on the belt. The load carrying side of the belt is often configured in a trough cross-sectional configuration so as to contain material loaded onto the belt.
To try and keep the belts centrally located (central tracking) it is known to adjust the alignment of either the drive roller or the return roller or both, and thereby keep the path travelling down its central path. However, if the belt is unevenly loaded, or if the belt stretches or wears in use, achievement of central tracking becomes more and more of a problem. A further problem is that it is often found that one part of the belt will tend to track centrally but other parts of the belt along its length tend to drift laterally to one or other side. For this reason it is standard practice to have an operator continuously adjusting the belt or the idlers over which the belt travels to try and achieve central tracking of the belt. High cost automatic pneumatic or hydraulic adjustors are known, but these are not always appropriate to use, particularly in high load mining operations.
To avoid this continual adjustment of the end idlers it is also known to install tracking idlers, which are also know as training idlers, along the length of the conveyor belt which will automatically slew about a vertical axis as the belt moves out of alignment to steer the belt back into its central path. Many different types of idlers of this type are known for tracking flat belts but that tracking or training of trough shaped belts constitutes more of a problem. The following patents indicate attempts to achieve tracking of trough shaped belts:
U.S. Pat. No. 2,815,851 PA1 U.S. Pat. No. 1,963,099 PA1 U.S. Pat. No. 2,561,641 PA1 U.S. Pat. No. 2,109,925 PA1 U.S. Pat. No. 1,705,558 PA1 a sub-frame adapted to be mounted to a support frame of a conveyor belt installation; PA1 at least one independently rotatable idler mounted for rotation on the sub-frame, the idler adapted to support a belt of the installation in position, the idler being aligned generally transverse to the length of the belt; PA1 the idler including a support shaft, an outer drum rotatably supported on the shaft, and a pivot assembly located within the drum defining a pivot axis about which the drum is pivotable relative to the shaft, the pivot axis being perpendicular to the belt which in use travels on the idler; PA1 contact means on at least one side of the idler adapted to be contacted by an edge region of a conveyor belt which has travelled from its central position towards that one side; PA1 the contact means being arranged to cause the drum of the idler to pivot about the pivot axis to steer the belt back to its central position. PA1 a sub-frame adapted to be mounted to the support frame of a conveyor belt installation; PA1 a plurality of independently rotatable idlers mounted for rotation on the sub-frame, the idlers adapted to support a belt of the installation in position, the idlers being aligned generally parallel to each other spaced apart from each other across the width of the belt, the sub-frame and idlers being mounted to the support frame generally transverse to the length of the belt; PA1 each of the idlers including a support shaft, an outer drum rotatably supported on the shaft, and a pivot assembly located within the drum defining a pivot axis about which the drum is pivotable relative to the shaft, the pivot axis being perpendicular to the belt which in use travels on the idler; PA1 adjacent idlers being linked together via link means adapted to transmit pivotal movement from one idler to the idler adjacent thereto in such a manner that as one idler pivots through a particular angle the idler adjacent thereto will be caused to pivot through substantially the same angle. PA1 at least one centre idler, and a pair of side idlers inclined to the centre idler on opposite ends thereof in a trough configuration; PA1 at least the centre idler including a support shaft, an outer drum rotatably supported on the shaft, and a pivot assembly located within PA1 the drum defining a pivot axis about which the drum is pivotable relative to the shaft, the pivot axis being generally perpendicular to the belt; PA1 contact means located at or adjacent the outer edge region of each of the side idlers connected to the centre idler and adapted to cause the outer drum of the centre idler to pivot about said pivot axis when a belt travelling on the assembly moves to one or other side of the assembly and into contact with the contact means, thereby causing the belt to be steered by the centre idler back to a centre position on the assembly. PA1 a sub-frame adapted to be mounted fixedly to a support frame of a conveyor belt installation; PA1 at least three rotatable idlers supported on the sub-frame including at least a centre idler and a pair of outer idlers, the idlers adapted to support a travelling belt in position, the idlers being aligned with their axes of rotation generally parallel to each other, the idlers being spaced apart from each other across the width of the belt; PA1 the sub-frame and idlers adapted to be mounted to the support frame generally transverse to the length of the belt, PA1 the centre one of the idlers including a support shaft, an outer drum which is rotatably supported on the shaft, and a pivot assembly located within the drum defining a pivot axis about which the drum is pivotable relative to the shaft, the pivot axis being generally perpendicular to the belt, the centre idler being supported on the sub-frame via its shaft; PA1 the outer idlers being independently rotatably mounted to the centre idler drum so that pivoting of the centre idler drum about its pivot axis will carry with it the outer idlers on either side thereof; PA1 the arrangement being such that a belt travelling on the assembly which runs off-centre to the extent that one longitudinal edge of the belt rides on the outer idler on that side to a greater extent than the opposite longitudinal edge of the belt is riding on the outer idler on opposite side thereof will create an uneven force on the assembly which will cause the idlers to pivot about the pivot axis and steer the belt back to its central path. PA1 a sub-frame adapted to be mounted fixedly to a support frame of a conveyor belt installation; PA1 a central idler supported on the support frame adapted to support a travelling belt, the idler adapted to be mounted to the support frame generally transverse to the length of the belt; PA1 the centre idler including a support shaft, an outer drum which is rotatably supported on the shaft, and a pivot assembly located within the drum defining a pivot axis about which the drum is pivotable relative to the shaft, the pivot axis being generally perpendicular to the belt, the centre idler being supported on the sub-frame via its shaft; PA1 a pair of arms on opposite sides of the centre idler, said arms being mounted to the central idler so as to pivot therewith; and PA1 wing brakes mounted at or near the free ends of each of the arms; PA1 said brakes being adapted to be contracted by a belt which travels over the central idler and shifts to a predetermined extent off its central path, the effect, when the brakes are so contacted being to cause the central idler to pivot about said pivot axis into an orientation adapted to steer the belt back to a central path.
The abovementioned patents all basically disclose an arrangement in which three idlers, which are mounted on a sub-frame in a normal trough-like configuration, are mounted so as to lie substantially transverse to the length and direction of travel of the belt. The sub-frame itself is mounted on a pivot axis which is perpendicular to the plane of the belt. Some mechanism is provided towards each edge of the assembly which the edge of the belt will contact as it shifts to one or other side of the assembly. By contacting the mechanism will cause the sub-frame to pivot on its pivot axis and thereby steer the belt back to its central position. Various problems exist, to a great or lesser extent with the different known systems. One problem, for example, is that the mechanism used to pivot the sub-frame has to be contacted by the edge of the belt in order to cause the necessary pivoting. The engagement of the edge of the belt against the mechanism tends to damage the edge of the belt, or the mechanism. Also, the manner in which the sub-frame is mounted to the main structure of the conveyor installation often means that adaptations are needed to be made to the conveyor installation which is undesirable.
A further problem with the tracking assemblies described in the abovementioned patents is that as the assembly pivots, the edge or "wing" idlers tend to move somewhat into the path of the belt which places significant strain on the assembly and decreases the efficacy of the tracking action.
It is desirable that where a training idler is to be installed, this can be done with a minimum of interruptions to the operation where the belt is located. It is also desirable that the training idler assembly is relatively expensive and uncomplicated in operation so that no special maintenance or skilled operator is required to install and maintain the training idler.